Recently, a microfiltration membrane or an ultrafiltration membrane is not only applied to a water treatment that manufactures industrial water or tap water from river water, wetlands water, groundwater, seawater, life drainage, industrial drainage, but also used in a wide variety of fields such as refinement and concentration-separation of food and pharmaceutical products. Above all, an external pressure type hollow fiber membrane module which performs filtering from an outer side to an inner side of the hollow fiber membrane is characterized in that a filtration membrane area per unit capacity of the module may be significantly greatly obtained, and is characterized by a high detergence using air scrubbing which cleans suspended matter on a hollow fiber membrane surface by vibrating the hollow fiber membrane surface using air supplied from a lower part toward an upper part of the hollow fiber membrane module, reverse running water washing which cleans suspended matter on a hollow fiber membrane surface by supplying filtrate or a cleaning liquid from an inner side toward an outer side of the hollow fiber membrane, and the like.
In addition, a hollow fiber membrane module utilized for food and pharmaceutical products use may be used for a membrane treatment system which treats a biologically active undiluted solution by performing sterilization using a hot liquid, sterilization using saturated water vapor, chemical cleaning using acid or alkali, and the like. To do so, thermal resistance and chemical resistance are required for all members included in the module in addition to the hollow fiber membrane.
Heretofore, from the viewpoint of thermal resistance and chemical resistance, a module case made of stainless steel is used, and a hollow fiber membrane module in which a hollow fiber membrane bundle is fixed by an adhesive resin using a heat-resistant epoxy resin as a main component is preferably used.
In the hollow fiber membrane module, when a heat cycle occurring due to a difference in temperature at the time of membrane filtration operation and at the time of saturated vapor sterilization acts on the module, peeling occurs due to a thermal expansion difference between the stainless steel case and the adhesion epoxy resin, and an undiluted solution which is raw water is mixed with filtrate, which is an issue.
On the other hand, a hollow fiber membrane module disclosed in Patent Literature 1 uses a fit fixation structure in which a concave portion and a convex portion are physically fitted such as a screwed joint as a joint between the stainless steel case and the adhesion epoxy resin, and uses a structure in which two circular sealing members are arranged on an inner circumference side and an outer circumference side of a boundary surface between an adhesive resin and a case on an end surface on an opening side of a hollow fiber membrane, thereby enabling an undiluted solution and filtrate to be separated even when a heat cycle is received.
However, in Patent Literature 1, the stainless steel case and the adhesion epoxy resin are physically fitted to each other. Thus, for example, an undiluted solution may flow into a gap and be deposited in the gap in an external pressure-type filtration, and an occurrence of a contamination due to a vapor sterilization defect is concerned in the gap where the undiluted solution flows and is deposited.
On the other hand, it is not preferable in terms of financial burden and environmental load when peeling occurs between the stainless steel case and the adhesion epoxy resin, and the entire module is discarded, and thus a variety of cartridge type hollow fiber membrane modules are being suggested.
In the cartridge type hollow fiber membrane module disclosed in Patent Literature 2, a circulating water passage is formed by liquid-tightly providing a headband shaped outer panel in an outer circumference of a case that accommodates a cartridge type hollow fiber membrane element, and cross flow filtration may be stably performed by forming a continuous hole allowing the circulating water passage to communicate with the inside.
However, in the configuration, an undiluted solution accumulates between the circulating water passage and the case, and liquid accumulation is formed, which may hinder sterilization using a hot liquid or sterilization using saturated water vapor.